1. Field of the Invention
The present invention relates to a fuel tank made of a thermoplastic synthetic resin and, more particularly, to a fuel tank of which an outer wall is formed by blow molding of the thermoplastic synthetic resin, and within which built-in parts are provided.
2. Description of Related Art
Conventionally, metallic fuel tanks have been used as fuel tanks for motor vehicles, etc., but, in recent years, fuel tanks made of thermoplastic synthetic resins have been used, because they are light in weight, no rust is generated therein, and they can be readily formed into desired configurations.
In many cases, the fuel tanks for use in motor vehicles, which are made of thermoplastic synthetic resins, have been formed by blow molding, because tubular bodies can be readily formed. With a blow molding method, a parison of a molten thermoplastic synthetic resin formed into a cylindrical configuration is extruded from an upper side of a mold, and air is blown into the parison while the parison is being held with the mold, thereby forming the fuel tanks.
On the other hand, in the blow molding method, it has been also required to provide built-in parts such as valves, baffle plates adapted to suppress noise caused by the flowing of fuel, etc. in an interior of the fuel tank.
To respond to this demand, there has been proposed a method of setting a built-in part in a resin frame, setting the resin frame within a mold, and bonding the resin frame to an inner surface of an outer wall of a fuel tank by blow molding, whereby the built-in part is mounted in an interior of the fuel tank (see published Japanese patent application No. Hei 1-301227, for example.)
In this case, however, since the built-in part is held with the resin frame, and is bonded to the inner surface of the outer wall of the fuel tank, an additional work of removing the resin frame is needed after blow molding, and in the case of small-sized built-in parts, the resin frames may become large so that the weight thereof may be increased.
In addition, in order to provide a built-in part in an interior of the fuel tank, there has been also effected such a process as is shown in FIGS. 1 and 2 (see published Japanese patent application No. Hei 6-143396, for example.).
More specifically, as shown in FIG. 1, a built-in part 10 is placed on a holding rod 12 before a parison 14 enters a blow mold 16, and after the blow mold 16 is opened, the built-in part 10 is positioned within the blow mold 16. Then, the parison 14 is lowered with the blow mold 16 left opened, thereby positioning the built-in part 10 in an interior of the parison 14.
Then, as shown in FIG. 2, press pins 18 are made to project from both sides of the blow mold 16 before the blow mold 16 is closed to press the parison 14 against side ends of the built-in part 10. At this time, an inner surface of the parison 14 has not been solidified so that the parison 14 and the side ends of the built-in part 10 can be fusion-bonded together.
And, the holding rod 12 is lowered, the blow mold 16 is closed, and air is blown into the blow mold 16 to perform blow molding.
In this case, abutment surfaces 20 formed at distal ends of the built-in part 10 for abutment with the parison 14, merely contact the inner surface of the parison 14, and the abutment surfaces 20 do not penetrate into the parison 14, whereby adhesion therebetween is week, and the fusion-bonding strength is not sufficiently large so that the parison 14 may peel from the built-in part 10 due to vibrations of fuel, expansions of fuel tanks, etc.
In addition, in order to increase the strength of the fuel tank, there has been also proposed to recess upper and lower portions of the outer wall thereof, and fusion-bond them over several locations thereof. In this case, however, since the outer wall is locally recessed and fusion-bonded together, the interior volume of the fuel tank is unfavorably reduced.
In order to overcome the above-described problem, as shown in FIG. 3, there has been also proposed a mounting member 24 for a built-in part, which has a plurality of arc-shaped elongated projections 26 on an abutment surface 22 thereof with a triangular cross-section (see published Japanese patent application No. 2009-132297, for example.). Air release grooves 28 are provided between adjacent elongated projections 26.
However, since the elongated projections 26 are formed long into an arc-shaped configuration so that when an impact and a bending stress are applied to an outer wall of a fuel tank, not the elongated projections 26 but the outer wall of the fuel tank may be deformed.